The present invention relates to refrigeration and heating, more particularly to closed and open loop refrigeration and heat pump systems which employ kinetic cooling of the working substance.
There is widespread use of mechanical refrigeration systems of the type which employ working fluid, or refrigerant, running in a closed loop. In a very common compression system, fluid, such as ammonia or Freon-12(trademark) dichlorofluoromethane gas is compressed, essentially adiabatically. The fluid is then cooled in a cooling coil, or condenser, so the heat of compression is discharged to a waste heat reservoir or sink, and the refrigerant is liquefied. The refrigerant is then expanded, as by passing it through an orifice or expansion valve connected to a lower pressure region. Thus, the refrigerant gas is cooled by the Joule-Thompson effect, as the liquid refrigerant is vaporized; and, it is then passed through a cooling coil, or evaporator, which is located in the region which is to be cooled. The refrigerant absorbs heat from the region. It is then flowed back to the compressor.
The thermodynamic cycle of such a typical system is commonly characterized as a reversed Brayton cycle. The compressor, which may be of any of a variety of mechanical types, is typically driven by an electric or other kind of motor.
A less common refrigeration system is the absorption type, founded on Dalton""s law of partial pressure of gas mixtures. An absorption system has similar elements to the compression system, but the compressor is replaced by a heater and generator. The refrigerant is a special combination of two gases, such as ammonia and hydrogen or lithium bromide and water. In the generator, heat causes differential separation of one gas from the other. Heat sources can be flames or a radiant source, such as solar energy. Such kinds of systems have tended to find use in locales where a reliable central source of electricity for motors is not available.
A disadvantage of the common prior art systems is that the refrigerants have qualities which are either noxious or environmentally disfavored. Another disadvantage is compressor noise and eventual wear when comparatively high system pressures are required. And of course, it is always an objective to increase the coefficient of performance of such systems.
In both of the above-described types of prior art systems, the refrigerant is liquefied, or condensed. It is thus subjected to a change in physical state, or phase. There are some relatively inefficient systems of the prior art wherein the refrigerant, such as air, does not liquefy. Such a refrigerant is simply subjected to different pressures and temperatures. In all aforementioned prior art instances, the gas molecules only undergo changes in translational energy, and there is no change in molecular state.
All refrigeration systems require some sort of net energy input to the system, to accomplish the desired work of moving energy (heat) from one point to another. In the prior art, the work energy (power to the compressor, or heat to the generator, as the case may be for the two representative types of prior art systems mentioned above) is imparted to the refrigerant in a way which raises the enthalpy of the working fluid at the point where work energy is imparted. And, as is well known in physics and engineering, when energy is imparted to fluid molecules as heat, or when there is inevitable heating of a gas during compression in accord with Boyle""s Law, the increase in temperature of the refrigerant gas is manifested as an increase in molecular translational energy. According to classical modeling, for the temperature ranges of interest relating to this patent application, such an increase in molecular energy of a fluid is manifested principally as an increase in the amplitude and frequency of translational motion of the molecules. As will be seen from the Description which follows, the present invention employs principles which differ from these traditional operational modes.
The present invention has relation to U.S. patent application Ser. No. 09/346,721, now U.S. Pat. No. 6,282,894, entitled xe2x80x9cEngines Driven by Laser Kinetic Coolingxe2x80x9d, filed on Jul. 2, 1999 by D. Smith, an applicant here. The related application describes a closed loop engine or prime mover, such as a turbine or positive displacement engine, which is powered by radiant energy, in particular by laser energy, delivered to the working fluid.
An object of the invention is to provide a heat transfer system and method, for cooling or heating things, which employs minimal moving parts and an environmentally friendly and relatively inexpensive working substance. A further object is to have the refrigeration and heating systems operate in closed and open loop modes, and with higher efficiencies than prior art systems provide. A further object of the invention is to employ electromagnetic radiation energy in refrigeration and heat pumping. A still further object is to optimize the operations of such new processes by utilizing kinetic cooling; to provide working substance gas mixtures which are particularly adapted for kinetic cooling; and to provide electromagnetic radiation energy sources and systems for achieving kinetic cooling which are more cost effective than lasers.
In accord with the invention, kinetic cooling of a working substance is used for refrigeration or heating of matter. Electromagnetic radiation, of one or more selected wavelengths, is impinged on a working substance, e.g., a gas mixture, contained within apparatus, to thereby cause the substance to be kinetically cooled. Kinetic cooling occurs when radiant electromagnetic energy causes molecules of a gas or other working substance to become excited. A significant number of molecules increase in energy from a first energy level to higher vibrational energy levels. Molecular collision processes induce corresponding restoration of thermodynamic equilibrium in the gas. The effect of the irradiation is to decrease the working substance temperature. When the invention is used for cooling, thermal energy or heat from the matter to be cooled is transferred to the kinetically cooled and excited working substance prior to its relaxation from its excited state, as it flows along a flow path and through a first heat exchanger. The heat is subsequently discharged from the working substance in a second heat exchanger, or by dumping of the working substance to a heat sink, according to whether a closed loop or open loop system is being operated.
In a closed loop embodiment referred to as a Type I system, recirculating gas is the working substance which flows along a closed loop gas flow path The means for kinetically cooling the gas is a mirrored cooling cell which channels the flowing gas as electromagnetic radiation impinges on it. The kinetically cooled gas is then quickly flowed to a first heat exchanger where heat from the environment or matter being cooled is transferred to the gas, thus raising the gas temperature. The gas is then flowed further downstream to a region where, with continued passage of time of flowing, natural relaxation (loss of vibrational energy) of the gas molecules occurs, according to a particular time function characteristic of the gas composition and system pressure. The relaxation also causes the gas to rise in temperature. The heat in the gas is then discharged from the working substance, either to a heat sink, or to a region where heating is desired, according to whether the system is being used for refrigeration (e.g., as is a common building space air conditioner) or for heating (e.g., as is a common building space heat pump). In one variation of a Type I refrigeration system, the working gas flows through a compressor, then a first heat exchanger for sensible cooling of the gas, then through a cooling cell for kinetic cooling, then through an expander, and then through a second heat exchanger where heat is absorbed by the gas from the thing being refrigerated.
In further accord with the invention, a closed loop system, called a Type II system, comprises a simple fan as the means for flowing gas. The fan greatly reduces energy consumption and increases Coefficient of Performance, compared to prior art reversed Brayton cycle systems.
In further accord with the invention, an open-end system, called a Type III system, comprises a means for kinetic cooling and a downstream heat exchanger for transferring heat from the matter being cooled to the working gas. The working gas with its acquired thermal energy is then discharged to a sink, i.e., the environment. As an example, atmospheric air is ingested into the cooling cell, then flowed through a heat exchanger, and then discharged back to atmosphere. An additive gas may be injected into the air flowing into the cooling cell, to make the working substance more amenable to kinetic cooling. In one application, the invention is used for cooling the interior of an automobile and the additive gas comprises carbon dioxide or other gas derived from the exhaust of the engine, such as an internal combustion engine or a fuel cell.
In further accord with the invention, the working substance in the cooling cell is impinged upon by electromagnetic radiation (e.g., light) from a source which provides one, or more than one, suitable gas-exciting wavelength. For example, a working fluid comprised of nitrogen and carbon dioxide is irradiated by pulsed or continuous laser light at 10.6 micron wavelength. The light source may be inside or outside the cooling cell. A light source of comparatively broad bandwidth of radiation may be used, such as light provided by a high intensity electric arc discharge, a black body source such as a resistance heating element, or the Sun. In another embodiment, radiation from such multi-spectral sources is filtered before passing through a cooling cell window into the cooling cell interior. For instance, for a selected working gas, only predominately 9-11 micron wavelengths are impinged on the working gas, to thus avoid sensible heating of the gas which is unbeneficial. The cooling cell typically has mirrors or other reflective means to increase the path length of a the electromagnetic energy beam, through the gas flowing within the cell, to thereby increase the extent of beam or energy absorption by the gas.
In the invention, the working substance is a fluid comprised of at least one substance, for example carbon dioxide, which is kinetically coolable, i.e., the working substance. The fluid responds significantly to radiation, by changing from a first energy level to a higher energy level, so that the molecules of the fluid are characterized by significant vibrational energy. In a preferred practice, a diatomic molecule gas, such as nitrogen, which has a certain relaxation time, is used in combination with a triatomic molecule gas, such as carbon dioxide, which has a comparatively shorter relaxation time.
In another aspect of the invention, a working gas comprises a mixture of radiation-responsive gas components, where the components respond differently to particular wavelengths of energy. Thus, the gas mixture absorbs energy at a greater multiplicity of wavelengths than does a single component gas. Such gas mixtures make it more feasible and efficient to use wider wavelength-band light sources. In one kind of such gas mixture, gases having different chemical properties are used. For instance, C02 and N02 are used in combination with N2; or N2O and C02 may be used with N2. In another kind of gas mixture, the components comprise two or more isotopic species of the same elementary chemical (molecular) composition gas. For instance, C12 and C3 isotopes may be respectively present in the two different species of carbon dioxide gas. In another example, the working substance mixture comprises a multiplicity of isotope-species of different chemical composition component gases.
The systems of the invention allow the use of common natural environment gases, such as C02 and N2. Such gases are already present in the atmosphere and are therefore largely benign environmentally, compared to the gases familiarly used in common prior art commercial refrigeration and heat pump systems, such as those using the reversed Brayton cycle systems. Refrigeration and heat pumping with the invention is characterized by high coefficients of performance. Because they employ radiant energy, the systems or the invention are useful for operation from sources which are located at some distance from the apparatus.
The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings.